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  Adaptive watermarkingUSPTO Application #: 20060072750Title: Adaptive watermarking Abstract: A method and apparatus (200) for embedding a watermark in an information signal bit-stream are described. The method comprises receiving a portion of an information signal bit-stream (MPEG2). A first copy of the received portion is stored in a first buffer (220). A second copy of the received portion is watermarked, and the resulting watermarked signal stored in a second buffer (240). At predetermined intervals, a check is performed to determine if the bit-rate of the received portion has been changed by being watermarked. If the check determines the bit-rate has changed, the first copy of the received portion from the first buffer is output. Otherwise the watermarked signal from the second buffer is output. (end of abstract) Agent: Philips Intellectual Property & Standards - Briarcliff Manor, NY, US Inventors: Frits Anthony Steenhof, Gerrit Cornelis Langelaar USPTO Applicaton #: 20060072750 - Class: 380201000 (USPTO) Related Patent Categories: Cryptography, Video Cryptography, Copy Protection Or Prevention The Patent Description & Claims data below is from USPTO Patent Application 20060072750. Brief Patent Description - Full Patent Description - Patent Application Claims
FIELD OF THE INVENTION [0001] The present invention relates to methods and apparatus suitable for embedding a watermark in an information signal bit-stream, and in particular is particularly suited, but not limited, to information watermarking signals which are compressed. A typical example of such a compressed information signal is an MPEG2 video signal. BACKGROUND OF THE INVENTION [0002] Watermarking of information signals is a technique for the transmission of additional data along with the signal. For instance, watermarking techniques can be used to embed copy write and copy control information into video signals. [0003] U.S. Pat. No. 5,809,139 describes a digital watermarking method and apparatus for the watermarking of a digital video signal in a compressed form. To allow the system to be used with transmission channels having strict bit-rate constraints, the system also includes bit-stream control to prevent an increase in the bit-rate of the video signal. For each transform coefficient of the video signal, it is determined whether more bits will be necessary to encode a watermarked version of the coefficient than an un-watermarked coefficient. If more bits are required to transmit a watermark coefficient, then the un-watermarked coefficient is output. Such a method can be used to watermark a MPEG2 video Elementary Stream (E.S.). [0004] Equally, a method described in WO 02/060182, by which a watermark is embedded by selectively discarding the smallest quantized DCT (Distribute Cosine Transform) coefficients, can be used to provide a watermarked signal that is either the same bit-rate as, or a lower bit-rate than, the original signal. This lower bit-rate can be raised back to the original bit-rate by accumulating a relatively large amount of data sufficient to form one or more packets, and stuffing the packet(s) with zero bits. [0005] However, such methods are not appropriate for watermarking information bit-streams that are defined on the system level, for instance a Transport Stream (T.S.), as for instance used in Digital Video Broadcasting (DVB), or a Program Stream (P.S.), as for instance used in Digital Versatile Disk (DVD). [0006] In T.S. and P.S., bit-rate control is more difficult because the elementary stream information is interrupted at random places by other data, such as other video stream(s), audio steam(s), system data, and timing data. In order to prevent distortion of the resulting video signal, it is important that the bit-rate control is such that the position of the start code in the compressed video stream does not change upon the watermarling applied. Equivalently, it is desirable that the number of bits between start codes does not change due to the watermark being applied to the signal. For instance, in MPEG a change of the number of bits between start codes would result in system timing errors and/or result in buffer over or under flow upon decoding of the bit-stream. [0007] It is an aim of embodiments of the present invention to provide methods and apparatus suitable for applying a watermark to an information bit-stream without changing the bit-rate of the information signal. [0008] It is a further aim of embodiments of the present invention to provide methods and apparatus for watermarking a Program Stream or a Transport Stream such that the position of start codes in the bit-stream does not change. SUMMARY OF THE INVENTION [0009] In a first aspect the present invention provides a method of embedding a watermark in an information signal bit-stream, the method comprising the steps of: receiving a portion of an information signal bit-stream; storing a first copy of the received portion in a first buffer; watermarking a second copy of the received portion; storing the resulting watermarked signal in a second buffer; performing a check at predetermined intervals to determine if the bit-rate of the received portion has been changed by being watermarked; and outputting the first copy of the received portion from the first buffer if the check determines the bit-rate has changed, otherwise outputting the watermarked signal from the second buffer. [0010] By utilising such a scheme, the bit-rate of the output signal can be maintained at the same bit-rate as the input signal. Further, by appropriate selection of the predetermined intervals, it is possible to ensure that positions of start codes in the bit-stream do not change. [0011] In another aspect, the present invention provides a computer program arranged to perform the method as described above. [0012] In a further aspect, the present invention provides a record carrier comprising a computer program as described above. [0013] In another aspect, the present invention provides a method of maling available for downloading a computer program as described above. [0014] In a further aspect the present invention provides a watermarked information signal formed according to the method as described above. [0015] In another aspect the present invention provides a record carrier comprising a watermarked information signal as described above. [0016] In a further aspect the present invention provides an apparatus for embedding a watermark in an information signal bit-stream, the apparatus comprising: a receiver for receiving a portion of an information signal bit-stream; a first buffer for storing a first copy of the received portion; a watermarker for watermarking a second copy of the received portion; a second buffer for storing the resulting watermarked signal; a controller arranged to perform a check at predetermined intervals to determine if the bit-rate of the received portion has been changed by the watermarking process; and a multiplexer arranged to output the first copy of the received portion from the first buffer if the check determines the bit-rate has changed, and otherwise to output the watermarked signal from the second buffer. [0017] Other aspects of the information will be apparent from the dependent claims. BRIEF DESCRIPTION OF THE DRAWINGS [0018] For a better understanding of the invention, and to show how embodiments of the same may be carried into effect, reference will now be made, by way of example, to the accompanying diagrammatic drawings in which: [0019] FIG. 1 illustrates start code positions at different levels of MPEG2 bit-streams: A is an Elementary Stream, B is a Packetised Elementary Stream, C1 is a Program Stream, and C2 is a Transport Stream; and [0020] FIG. 2 is a schematic diagram of a remarking apparatus in accordance with an embodiment of the present invention. Continue reading... Full patent description for Adaptive watermarking Brief Patent Description - Full Patent Description - Patent Application Claims Click on the above for other options relating to this Adaptive watermarking patent application. ###  How KEYWORD MONITOR works... a FREE service from FreshPatents1. Sign up (takes 30 seconds). 2. Fill in the keywords to be monitored. 3. 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